1. Field of the Invention
The present invention relates to a controller for a motor that carries out field control of a permanent magnet field type rotary motor by changing the phase difference between two rotors disposed concentrically.
2. Description of the Related Art
There has been known a motor that comprises a permanent magnet field type rotary motor that has a first rotor and a second rotor concentrically disposed around a rotating shaft and carries out field weakening control by changing the phase difference between the first rotor and the second rotor according to the rotational velocity to change the induced voltage constant of the motor (see Japanese publication of unexamined patent application No. 2002-204541).
In such a conventional motor, the first rotor and the second rotor are connected via a member that is displaced in the radial direction by the action of a centrifugal force. The motor is configured so that, when the motor is halted, the magnetic pole of the permanent magnet on the first rotor and the magnetic pole of the permanent magnetic pole on the second rotor are oriented in the same direction, and thus the magnetic flux of the field is maximized (the induced voltage constant of the motor is maximized). In addition, the motor is configured so that, as the rotational velocity of the motor increases, the phase difference between the first rotor and the second rotor increases by the action of the centrifugal force, and thus the magnetic flux of the field decreases (the induced voltage constant of the motor decreases).
FIG. 22 shows a region for which field weakening of the motor is required. In this drawing, the axis of ordinates indicates the output torque Tr, and the axis of abscissas indicates the number of revolutions N. Reference character “u” in FIG. 22 denotes an orthogonal line of the motor (a line connecting points at which the phase voltage of the motor equals to the power supply voltage when the motor operates without the field weakening control and determined depending on the combination of the number of revolutions and the output torque). In this drawing, reference character X denotes a region for which the field weakening is not required, and reference character Y denotes a region for which the field weakening is required.
As shown in FIG. 22, the region Y for which the field weakening is required is determined by the number of revolutions N and the output torque Tr of the motor. Therefore, the conventional field weakening control that relies merely on the number of revolutions has a disadvantage that the induced voltage constant of the motor is changed excessively or insufficiently with respect to the required amount of field weakening control.
In addition, since the induced voltage constant cannot be changed independently of the number of revolutions of the motor, there is a disadvantage that an appropriate induced voltage constant cannot be set by taking into account operational conditions other than the number of revolutions, such as limitations on the output torque of the motor and the current that can be supplied, and thus the controllable range of the motor is narrow.
The present invention has been made in view of such circumstances, and an object of the present invention is to provide a controller for a motor that can appropriately set the induced voltage constant of a motor of a double rotor type according to the operational state of the motor and expand the controllable range of the motor.